The invention relates to electrochemical deposition or electroplating methods, and systems for removal of unwanted deposits resulting from electrochemical deposition or electroplating processes.
In semiconductor processes, multiple processes such a chemical vapor deposition (CVD), physical vapor deposition (PVD), and electroplating are performed in series on a substrate such as a semiconductor wafer. After electroplating is performed, edge bead removal (EBR) systems remove edge beads and other layers remaining on the substrates.
Modern metal electroplating can be can be accomplished by a variety of methods. Relatively high electrical conductivity, high electromagnetic resistance, good thermal conductivity, and availability in a highly pure form make copper and its alloys a choice electroplating metal. Typically, electroplating copper or other metals and alloys involves initially depositing a thin seed layer (having an approximate thickness of 2000 Angstroms) of a conductive material over the surface of the substrate including the features formed on the substrate. A layer is then plated onto the seed layer by applying an electric charge applied across the seed layer. The seed layer having an electric charge applied thereto attracts metal ions. The deposited layers and the dielectric layers can then be planarized to define a conductive interconnect feature, such as by chemical mechanical polishing (CMP).
During electroplating, metal ions contained in the electrolyte solution deposit on those substrate locations that electrolyte solution contacts that are covered by the seed layer. The seed layer is usually deposited on the front side of the substrate, however the seed layer may extend to the edge or the backside of the substrate. As such, metal may deposit on certain front side, edge, or backside locations that such metal depositions are not desired, as now described.
FIG. 2A shows a cross sectional view of one embodiment of an edge of a substrate 22 including a bevel edge 33, a seed layer 34 deposited on the substrate, and an electroplated conductive metal layer 38 deposited on the substrate. During processing of the substrate, the seed layer 34 is formed on a plating surface of the substrate (the plating surface faces downward in FIG. 2A). The seed layer stops a short distance from the bevel edge 33. A conductive metal layer is then deposited on the seed layer by an electroplating process. The conductive metal layer in FIG. 2A does not form on any portion of the substrate that does not have a seed layer. In the embodiment shown in FIG. 2A, an excess deposit buildup, known as an edge bead 36, forms at the edge of the electroplated layer. The edge bead typically results from locally higher current densities at the edge of the seed layer 34 and usually forms within 2-5 mm from the edge of the substrate. Removal of the edge bead from the substrate is desired to ensure uniform thickness of the conductive metal layer on the substrate 22.
FIG. 2B shows a cross sectional view of another embodiment of an edge of a substrate 22 including the bevel edge 33, the seed layer 34 deposited on the substrate, and the electroplated conductive metal layer 38 in FIG. 2A. In this embodiment, the seed layer 34 covers the front side 35 of the substrate, both bevels 33 on the edge, and for a small distance on the backside 42 of the substrate. This type of seed layer is known as a full coverage seed layer. Metal deposits form on those seed layer surfaces that are exposed to electrolyte solution during electroplating. When a full-coverage seed layer is applied to a substrate, removing the edge bead 36 following the electroplating process is often desired. Removing the deposited layers on the seed layer that occur on the backside and/or edge of the substrate on the full coverage seed layers limit contamination from these layers deposited on the backside of the substrate.
FIG. 3 shows a cross sectional view of yet another embodiment of an edge of a substrate 22 including the bevel edge 33, the seed layer 34 deposited on the substrate, and the electroplated conductive metal layer 38 deposited on the substrate. The electoplated conductive metal layer 38 includes a separated edge deposit 39. Such a separated edge deposit 39 may form on a substrate following electroplating. The separated edge deposit 39 of the seed layer typically forms within 2-5 mm from the deposited edge material. The separated edge deposit often separates from the substrate 22 since the separated edge deposit is not secured to the seed layer that would attach the separated edge deposit to the substrate. A separated edge deposit 39 often tears off during subsequent processing such as chemical mechanical planarization (CMP). The CMP pads that contain material of the separated edge deposit 39 may abrade and damage the substrate during CMP. CMP pads that contain embedded particles may severely damage (by scratching) any wafer to which they contact.
Therefore, during electroplating copper contamination can form on the front, the backside, or the edge of the substrate. Such metal deposition at undesired locations occur from full coverage seed layer wrapping around to the backside, small deposits of electroplated copper on the backside of the substrate, or the copper from the wet electrolyte solution drying on the backside of the substrate. The existence of copper contamination on the backside of the substrate can degrade the performance of an electronic device that uses a portion of the wafer because of altered properties of the substrate. Providing a system by which the copper contamination can be removed from the backside or the edge of the substrate following the metal deposition is desirable.
Edge bead removal (EBR) systems remove the aforementioned edge bead, the separated deposited layer, or certain other undesired deposited layers on the substrate. Nozzles in the EBR systems can be adjusted to direct etchant (that removes the deposits) and/or rinse water at desired locations on the substrate. EBR systems therefore can apply a variety of chemicals at an electroplated substrate where the undesired deposits are located. The chemicals used in EBR systems comprise, for example, a mixture including a prescribed ratio of acid mixed with an oxidizer and deionized water.
Chemicals used in prior EBR systems are mixed in a batch to form an etchant. To limit the effort required to mix a large number of batches frequently, the individual batch sizes are large. The batch is maintained until the etchant is used or until the etchant becomes unusable. The usable lifetime of the etchant in EBR systems varies depending on such parameters as the specific chemicals and amounts of each chemical mixed to form the etchant, the temperature at which the etchant is stored, and the pressure applied to the etchant. However, once the etchant becomes unusable, the etchant must be disposed of and a new batch of etchant must be prepared. One embodiment of etchant used for copper electroplating processes becomes increasingly unstable at higher EBR system temperatures. Unfortunately, etch rates of the chemicals used in EBR systems typically increase with higher temperatures. When operators increase the temperature of the EBR system to increase throughput based on the higher etch rates, the time until each batch of etchant becomes altered or unstable diminishes.
It is desired to maximize throughput in EBR systems since the EBR system represents only one of a large number of expensive processes that are utilized in expensive semiconductor processing systems. The EBR system cannot be used for deposition removal purposes when a new batch of chemicals is being mixed therein to form etchant. Presently, batches of chemicals in EBR systems are mixed by diffusion, so some time is necessary after a large batch is mixed for the chemicals to properly mix into etchant. In an effort to limit down time on an EBR system, the batches of etchant are mixed in a large volume (1 to 4 liters). Such large batches of etchant are difficult to dispose of after the etchant becomes unstable. In addition, some time is necessary to clean the unstable etchant from that equipment used to store, and/or dispense the chemicals.
Therefore, there is a need to provide an EBR device including a mixing tank, where the EBR device mixes chemicals into etchant at or near where the etchant is being used in an amount that can be used by the EBR device.
The invention generally relates to edge bead removal systems and associated methods that remove unwanted deposited metal from a substrate. An apparatus and associated method supplies etchant to an edge bead removal chamber. The apparatus includes an etchant tank that is capable of storing etchant, a sensor that senses the sensed level of etchant that is contained in the etchant tank, and a mixing tank that mixes one or more chemical components into etchant that is supplied to the etchant tank in response to the sensed level. The present invention is especially applicable to edge bead removal systems, including for example, spin-rinse-dry systems.